Playing Against Type: Until then, Michael J. Fox was mostly known for his comedy roles and for playing Marty McFly in Back to the Future. Playing a self-destructive cokehead was quite a change for him.
The Other Marty: When the original director Joyce Chopra was fired and replaced with James Bridges, he recast most of the principal cast except for Dianne Wiest and (ironically considering he was partially responsible for the trope namer) Michael J. Fox.
Shortly after it was optioned, McInerney wrote a script, and while it wasn't perfect it was enough to get Joel Schumacher to commit to the project as director, with Jerry Weintraub producing. After it was shopped around to many of the early '80s Brat Packers like Judd Nelson and Emilio Estevez, Tom Cruise signed on for the lead.
Weintraub became production chief at MGM/UA, and took the project with him. Since that meant he couldn't/wouldn't be able to produce it, he looked around for another producer. Sydney Pollack and Mark Rosenberg agreed to do it, but wanted a rewrite of the script. A new writer began working on it, but Cruise and Schumacher couldn't wait any longer, and left for other projects.
Then Weintraub left UA. The film went from Development Purgatory to Development Hell for months while all the legal issues were worked out. For a long time it wasn't clear whether the film would stay with UA or Weintraub.
Months later it was settled, with the studio retaining the film. Pollack and Rosenberg hired Joyce Chopra, who had recently gone from documentaries to features with the well-received Smooth Talk, to direct. She and her husband began work on yet another draft of the script, pne that departed significantly from the novel. The plan was to shoot the film in Toronto and cast an unknown in the lead. But Michael J. Fox responded positively to Chopra's requests, and agreed to play the part, also recommending his friend and countryman Kiefer Sutherland for the supporting role of Tad Allagash. So the budget went up, and filming could take place in New York where the novel had been set, albeit only within a ten-week window before Fox had to return to LA for the next season of Family Ties.
Things quickly went to hell on location. Chopra spent lots of time planning her shots and quickly fell behind schedule. She also reportedly freaked out one day when Fox's fans began congregating around the set, and the producers began to wonder if she was up to the job, causing friction between her and them. Friction with McInerney over her script led her to ban him from the set as well.
The studio didn't like the dailies it was seeing, not in the least because that was how the executives learned how Chopra and her husband had made so many changes to the story, such as writing the main character's drug use out. While there is still disagreement on whether Chopra and her husband did that on their own initiative or at the producers' behest, everyone agreed that it was done with the same motive—protecting Fox's public image.
A possible directors' strike was in the offing, complicating things even more. UA made the rare decision to fire Chopra. James Bridges took the call on a Friday, saw Chopra's footage, and agreed to take over and finish the film on an abbreviated schedule. He wrote another draft of the script and recast all but two of the supporting roles. Those actors took the part based on a reading of the novel, since there was no script at the time. Eventually Bridges and McInerney wrote the version, basically a rewrite of the novelist's first draft, that finally became the shooting script. They had agreed to share credit but the WGA awarded it all to McInerney. They were still nervous enough about Fox's image that they wrote and shot an alternate ending, in which the main character shows his girlfriend the eponymous novel he just wrote.
The final film received lukewarm reviews from critics, whose complaints reflected the by-then-well-known production difficulties. Fox seemed too young for the part, but Phoebe Cates was even more miscast as his ex-wife, whom one critic described as "the least convincing fashion model, ever." Donald Fagen's music seemed to be filler. Richard Schickel said, perceptively, that " [it looks] like something that has been kicking around too long in the dead-letter office."
What Could Have Been: See above. Many critics said Cruise would have been a much more believable Jamie.